1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a liquid crystal display that realizes full color without using color filters in sub-pixels by sequentially providing different colors of light to the display.
2. Description of the Related Art
Generally, liquid crystal displays (LCD""s) tend toward wider and wider application by virtue of their characteristics such as low weight, thin form factor, and low power consumption. Accordingly, LCD""s have been used for office automation equipment, video/audio equipment, etc. The LCD controls an amount of transmitted light in response to data signals applied to a number of control switches arranged in a matrix, to display a desired picture on the screen.
Referring to FIG. 1, the conventional LCD includes a back light unit 10 for generating and uniformly supplying a light beam to the liquid crystal panel 50. The liquid crystal panel 50 includes a lower polarizer 22 arranged at the upper portion of back light unit 10 to change a polarization characteristic of the light beam. A lower substrate 24 is arranged on the lower polarizer 22, and thin film transistors (TFT""s) 38 for applying a signal controlling a transmitted amount of the light beam are arranged in a matrix configuration. A liquid crystal layer 28 is provided at the upper portion of the lower substrate 24, and a common electrode layer 30 is provided on the liquid crystal layer 28. Color filter layers 36 are provided at the upper portion of the common electrode layer 30. An upper substrate 32 is provided on the color filter layers 36, and an upper polarizer 34 is arranged on the upper substrate 32 to convert a polarization characteristic of the light beam.
The back light unit 10 consists of a light source (not shown) for generating a light beam, a light guide (not shown) for uniformly guiding the light beam from the light source into a liquid crystal panel, and a reflector (not shown) arranged at the lower portion of the light guide to reflect a light beam from the bottom or side surfaces of the light guide toward the liquid crystal panel 50. By such a configuration, a light beam from the back light unit 10 progresses uniformly toward the liquid crystal panel 50. An exemplary energy distribution spectrum of a white light beam generated from the back light unit 10 is illustrated in FIG. 2.
The white light beam going from the back light unit 10 into the liquid crystal panel 50 is polarized by the lower polarizer 22. When the polarized light beam passes through a liquid crystal 28 controlled by the TFT 38, the polarization state of the polarized light beam is changed. More specifically, if the TFT 38 is turned on, then an image signal is applied via the TFT 38 to a pixel electrode 26. At this time, the liquid crystal 28 has a different orientation state in response to a potential between the pixel electrode 26 and the common electrode 30. A light beam changed in a polarization state by virtue of the liquid crystal layer 28 passes through the color filter layer 36, which transmits only wavelengths of light (i.e., colors) corresponding to each color filter element.
An exemplary spectrum of a light beam transmitted by the color filters is illustrated in FIG. 3. As shown in FIG. 4, one pixel 42 has sub-pixels 40 corresponding to red (R), green (G) and blue (B) colors. In other words, the three sub-pixels 40 make up a single pixel 42. As described above, a light beam transformed into a desired color by the color filter layer 36 passes through the upper substrate 32, and thereafter goes into the upper polarizer 34 to display a picture corresponding to an image signal.
The conventional color-filter LCD has a high manufacturing cost because the color filter material is expensive. Also, the conventional color-filter LCD has a problem that a resolution of a displayed image is deteriorated, since one pixel consists of three sub-pixels. Also, a production yield is lower, since a process of configuring the sub-pixels and a process of forming the color filter layers are additionally required. In order to solve these problems, a color-filterless LCD employing a sequential lighting system as shown in FIG. 5 has been suggested. As used herein, the term xe2x80x9ccolor-filterlessxe2x80x9d refers to a display that realizes full color without using color filters in sub-pixels of a liquid crystal panel, e.g., as shown in FIG. 4.
Referring to FIG. 5, the conventional color-filterless LCD includes three primary color light sources 12R, 12G and 12B turned on sequentially to generate sequential light beams corresponding to R, G and B colors. An optical medium 13 uniformly distributes the sequential light beams from the light sources. The liquid crystal panel 50 is not provided with any color filters. In order to implement a color image from such a structure, the back light unit 10 is provided with the three primary light sources 12R, 12G and 12B. In this case, a reflector (not shown) is arranged under the optical medium 13 and the three primary color light sources 12R, 12G and 12B. A diffusing sheet 66 and the like are arranged on the optical medium.
A method of driving the color-filterless LCD employing a sequential lighting system will be described below in conjunction with FIG. 6. As shown in FIG. 6, in order to display an image 6 in color, an R light beam is transmitted by a portion of the liquid crystal panel 50 corresponding to an R color of the entire image. In turn, a G light beam is transmitted by a portion corresponding to a G color of the entire image. Finally, a B light beam is transmitted by a portion corresponding to a B color of the entire image.
In order to realize a full color image, the three primary color light sources are sequentially turned on color-by-color, and the pixels of the liquid crystal panel 50 are controlled to have a transmissivity corresponding to a color brightness of the turned-on light source. When any one of the three color light sources 12R, 12G, and 12B has been turned on, other color light sources are turned off or have a minimum brightness. When such sequential turned-on times are controlled to have a very short time interval, an observer does not sense a turning on and off of the displayed image, but views a full color image. Since the color-filterless LCD shown in FIG. 5 does not use any color filters, a manufacturing cost of the liquid crystal panel can be reduced. Also, because it permits an expression of a picture corresponding to an image signal using only single pixels without any sub-pixels, the LCD""s resolution, brightness and aperture ratio can be improved.
The conventional color-filterless LCD may be configured by a back light directly under the liquid crystal panel 50 as shown in FIG. 5, and the back light includes a light guide 14 under the liquid crystal panel 50 and lamps to the side of the light guide 14 as shown in FIGS. 7A and 7B. However, since the conventional color-filterless LCD has to turn on the three primary color independent light sources during a short period, the number of light sources as well as a size of the light source driver is increased. Thus, the conventional color-filterless LCD has problems of a complex driving system and a short life. Also, the back light under the liquid crystal panel 50 has a disadvantage in that it has large thickness and high power consumption. On the other hand, the back light to the side of liquid crystal panel 50 can achieve a thin form factor, low weight and low power consumption, but has a difficulty in arranging the three primary color light sources efficiently as shown in FIG. 7B. As a result, a novel strategy for overcoming the above-mentioned problems has been required.
Accordingly, it is an object of the present invention to overcome one or more disadvantages of the conventional displays noted above.
In order to achieve these and other objects of the invention, a liquid crystal display device according to an embodiment of the present invention includes a liquid crystal panel; a light source to generate light for illuminating the liquid crystal panel; a light guide to guide light from the light source to the liquid crystal panel; and a three primary color selector optically coupled to the light source to sequentially generate three primary color light beams from incident light from the light source.
A back light unit according to another embodiment of the present invention includes a light source to generate light; a light guide to guide light from the light source; and a color selector arranged in an optical path of the light source to sequentially transmit a plurality of colors within incident light from the light source.